The present invention relates to an apparatus for controlling the supply of developing agent to a developer. Particularly, this invention relates to an apparatus for controlling the supply of developing agent to a developer used in an image forming apparatus such as a plain paper color copy machine and a printer, for printing data transferred from an image-data supplying device such as a personal computer and a digital camera, on plain papers or OHP sheets.
Developers used in image forming apparatus are usually equipped with an automatic supplying mechanism for toner to be consumed in printing. A popular developing technique is two-component developing using developing agent including toner to be used in printing characters and carriers having electrostatic property. Repeated image-forming operations require the supply of toner to cover a detected consumed amount while the carrier amount is almost constant in alternately-performed charging and charge-removing operations.
The amount of toner to be consumed varies between printing a large number of characters and information with a large white area such as a picture and a graph on a sheet of paper. Several factors such as a low printing rate and a high intermittent-printing rate cause variation in toner-consuming rate versus developer-driving time. Discussed below is a relation between a toner amount to be consumed and a developer-driving time.
Repeated intermittent-printing operations cause variation in toner amount to be consumed per developer-driving time due to unproductive driving. Unproductive driving periods exist before the beginning of and also after the end of image-forming operation, in which a developer motor is running for driving the developer while no toner is being consumed. The more the intermittent printing is performed with a pause for every given number of sheet, such as, fifth and second sheet, against continuous printing over a relatively large number of sheets, the more the toner-shaking amount is increased against developer-driving time. Therefore, toner-consuming rate versus developer-driving time depends on the combination of printing rate and intermittent-printing level.
Toner-supply control for conventional developers is disclosed, for example, in Japanese Unexamined Patent Publication No. 5-88554. In detail, a toner supply amount is estimated based on deviation and rate of change in toner density detected by a toner sensor from a reference level. The estimated toner amount is supplied by a supplier per specific number of pixels counted by a counter. This technique offers the supply of appropriate amount of toner in accordance with a consuming amount of developing agent, thus achieving constant developing-agent density in a developer.
The known toner-supply control technique uses toner density and printing rate as basic factors, thus could cause change in developing-agent charged amount if a developer is driven with no toner consumption in a developing agent in the developer. This phenomenon depends on physical properties of toner in the developing agent. In detail, rotation of a developer motor in a developer running with no toner consumption could cause increase in developing-agent charged amount over an appropriate level due to low printing rate or intermittent printing, thus lowering printed-image density, in use of a developing agent including toner that has a tendency of increasing its charged amount. The decrease in printed-image density will not be constant but vary in accordance with printing rate or intermittent printing. Therefore, this known toner-supply control technique poses a problem of unstable image formation.
A purpose of the present invention is to provide an apparatus for controlling the supply of developing agent to a developer, achieving stable image formation independent of printing rate and intermittent printing, using data on the amount of toner to be consumed in unit of real time obtained based on printing rate and actual developer-driving time.
A developing-agent supply control apparatus for a developer in a first basic configuration according to the present invention for fulfilling the purpose is an apparatus for controlling the supply of a developing agent, installed in a developer, comprising: a developing-agent amount detector to detect an amount of the developing agent consumed by the developer; a driving-time detector to detect a driving time for actually shaking the developing agent provided in the developer; a developing-agent density calculator to calculate an actual density of the developing agent in the developer based on the consumed amount of the developing agent detected by the developing-agent amount detector and the actual driving time detected by the driving-time detector; a developing-agent amount controller to compare the actual density calculated by the developing-agent density calculator and a reference developing-agent density to perform forcible supply of the developing agent when the actual density is lower than the reference density whereas forcible consumption of the developing agent when the actual density is equal to or higher than the reference density; and a consumed-amount adjuster to adjust the consumed amount of the developing agent per unit of time under control by the developing-agent amount controller.
Moreover, a method of controlling the supply of a developing agent for a developer in a second basic configuration according to the present invention, comprising the steps of: a developing-agent amount detecting step to detect an amount of the developing agent consumed by the developer; a driving-time detecting step to detect a driving time for actually shaking the developing agent provided in the developer; a developing-agent density calculating step to calculate an actual density of the developing agent in the developer based on the consumed amount of the developing agent detected by the developing-agent amount detector and the actual driving time detected by the driving-time detector; a developing-agent amount controlling step to compare the actual density calculated by the developing-agent density calculator and a reference developing-agent density to perform forcible supply of the developing agent when the actual density is lower than the reference density whereas forcible consumption of the developing agent when the actual density is equal to or higher than the reference density; and a consumed-amount adjusting step to adjust the consumed amount of the developing agent per unit of time under control in the developing-agent amount controlling step.
Furthermore, an apparatus for controlling the supply of a developing agent, installed in a developer, in a third basic configuration according to the present invention, comprising: means for detecting an amount of the developing agent consumed by the developer; means for detecting a driving time for actually shaking the developing agent provided in the developer; means for calculating an actual density of the developing agent in the developer based on the consumed amount of the developing agent detected by the developing-agent amount detecting means and the actual driving time detected by the driving-time detecting means; means for comparing the actual density calculated by the developing-agent density calculating means and a reference developing-agent density to perform forcible supply of the developing agent when the actual density is lower than the reference density whereas forcible consumption of the developing agent when the actual density is equal to or higher than the reference density; and means for adjusting the consumed amount of the developing agent per unit of time under control by the developing-agent amount controlling means.